1. Field of the Invention
This invention relates to an apparatus and a method for making multi-throw crankshafts, and more particularly, to method and apparatus for heating of metal rod stock to a forming temperature, and then bending the heated rod at desired locations along its length, in different directions, to form a plurality of parallel throws.
2. Description of Related Art
It is known in the prior art to form multiple-throw crankshafts by forging operations wherein rod or bar stock is heated and bent to form the throws. U.S. Pat. Nos. 2,555,695 and 2,676,229 disclose apparatus for electrically heating bar stock and then bending the heated portions to form an offset throw section. However, the apparatus illustrated therein is limited to the formation of a crankshaft wherein all of the throws lie in a single plane, unless separate heating, forming and cooling cycles are carried out with some manual adjusting of the rotary positioning of the bar between the performance of such cycles. U.S. Pat. No. 4,030,172 discloses apparatus for forming multi-throw crankshafts from a metal rod in a one-shot, automatic operation regardless of the desired position of the respective throws at any location 360.degree. about the axis thereof.
The crankshaft may have to be used in various applications, one of which is in farm equipment. Preferably, each of the throws is to be parallel, throughout its length, to the horizontal rotational axis defined by the ends of the crankshaft. Thus, a throw should not be high at one end or low at another end, relative the horizontal rotational axis for the crankshaft. Likewise, in a horizontal direction, one end of the throw should not be nearer to the horizontal rotational axis than the other end of the throw. High or low, as well as near or far ends on the throws, cause undue localized forces and/or wear which could be eliminated or reduced, if the throw had its axis and surfaces more perfectly parallel to the rotational axis of the crankshaft. The throws are formed while the bar is heated to a temperature of 1800.degree. to 1900.degree. and then the crankshaft is allowed to cool. Because of the substantial bending and the formation of corners where the throws join the rest of the crankshaft, differential cooling occurs and differential shrinking occurs, and the direction of shrinking pulls the throws from parallel alignment with the rotational axis. Also, apparatus disclosed in the aforementioned patent is used to make crankshafts of different lengths, different numbers of throws, and different angular positions of the throws with different diameters of rod. Hence, the differential shrinking and pulling in different directions, and the adjustments for different numbers of throws and sizes of rods, makes it difficult to keep the precise alignment of parallelism for each of the throws with respect to the rotational axis. Thus, there is a need for the ability, in such a crankshaft forming machine, to be able to make adjustments and corrections to assure the desired parallelism for each of the throws irrespective of the cause of such non-parallelism.
The crankshafts are bent with forming heads that move axially as the throws are made and the crankshaft is shortened, and the forming heads include carriages and subcarriages movable in directions orthogonal to one another, so as to displace the throw at a predetermined angle about a spectrum of 360.degree.. Thus, the crankshaft may have throws at 15.degree. or 195.degree. etc. about the rotational axis. All of these complex and simultaneous movements are controlled, but with the variables and tolerances involved, it is not unexpected that the throws might not be in exact parallelism from one end to the other end thereof. The ability to make such adjustments should not be so difficult or cumbersome that the operator cannot make the adjustments with reasonable speed and understanding of how the adjustments are made. Moreover, the adjustments are made with relatively simple and inexpensive mechanisms that can withstand the heat and high forces involved in bending the crankshafts.
Another aspect of the apparatus disclosed in U.S. Pat. No. 4,030,172 that could stand improvement, is the manner of clamping and opening and closing the split halves of the forming heads which grip the rod at the locations the throws are to be made. It has been found that more uniform electrical heating of the rod is achieved at the throws, if the clamping pressure is increased. With the pivoted heads disclosed in this patent, the upper head is held closed by a pair of locking pins inserted into a pair of holes in a tongue attached to the upper head. There is no adjustment of this clamping force and of course, locking bolts and holes may wear out with continued use, causing a decrease in clamping force. Decreased clamping force appears to allow more localized spots of differential heating which can be reduced with higher clamping forces. The prior opening mechanism for pivoting upwardly the upper half of the forming head, as disclosed in U.S. Pat. No. 4,030,172, included a slide bar which moved a cam that cammed against an ear on the upper half. Such camming experienced a high degree of wear. Thus, there is a need to provide a new and improved manner of opening and closing the forming heads, and in applying large clamping forces to the rod to overcome localized heating areas on the clamped portions of the rod.